The present invention relates to a phosphor panel with a protective layer.
A well-known use of phosphors is in the production of X-ray images. In a conventional radiographic system an X-ray radiograph is obtained by X-rays transmitted image-wise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) wherein phosphor particles absorb the transmitted X-rays and convert them into visible light and/or ultraviolet radiation to which a photographic film is more sensitive than to the direct impact of X-rays.
According to another method of recording and reproducing an X-ray pattern as disclosed e.g. in U.S. Pat. No. 3,859,527 a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel, is exposed to incident pattern-wise modulated X-ray beam and as a result thereof temporarily stores energy contained in the X-ray radiation pattern. At some interval after the exposure, a beam of visible or infra-red light scans the panel to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which can be processed to produce a visible image. For this purpose, the phosphor should store as much as possible of the incident X-ray energy and emit as little as possible of the stored energy until stimulated by the scanning beam. This is called xe2x80x9cdigital radiographyxe2x80x9d or xe2x80x9ccomputed radiographyxe2x80x9d.
In both kinds of radiography it is preferred to be able to choose the phosphor that will be used on the basis of its speed and image quality without having to bother about its hygroscopicity.
Therefore it is highly desired to have the possibility of producing a phosphor panel, be it for use in direct radiography or in computed radiography, that is impervious to water vapor. In U.S. Pat. No. 4,741,993 a radiation image storage panel is disclosed having at least one stimulable phosphor layer on a support and a protective layer provided on the stimulable phosphor layer, wherein the protective layer comprises at least two layers of which regains under a relative humidity of 90% on a sorption isotherm at 25xc2x0 C. are different by 0.5% or more. According to this invention, a radiation image storage panel which has good humidity resistance and can be used for a long term is obtained. Although a protective layer as disclosed in U.S. Pat. No. 4,741,993 does provide good humidity protection, the need for providing phosphor panels with even better humidity resistance is still present.
Use of parylene layers as humidity protective layers in photo-stimulable phosphor screens has been disclosed in e.g. EP-Application No. 01000401.8, filed Aug. 23, 2001. Also in DE-A-196 25 912 and GB-A-2 287 864 phosphor screens containing a parylene layer are disclosed.
Although screens prepared according to the disclosures above do yield screens with acceptable to very good overall quality, the need for a phosphor screen combining good humidity resistance and good resistance against physical damage during use is still present.
It is an object of the invention to provide a phosphor screen or panel with very high humidity resistance.
It is further object of the invention to provide a binderless storage phosphor panel with very high humidity resistance.
The above mentioned objects are realized by providing a phosphor panel having the specific features defined in claim 1. Specific features for preferred embodiments of the invention are disclosed in the dependent claims.
Further advantages and embodiments of the present invention will become apparent from the following description.